Process for the production of 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester, and process for the production of quinacridone from said ester as intermediate

ABSTRACT

A process for producing 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester having a high purity from 1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) at high yields for a short period of time; a process for producing quinacridone of which the byproduct content is small, from the above 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester; and a process for producing quinacridone of which the particle diameter is adjusted as desired, from the above 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester without adding a step of forming a pigment.

This is a divisional application of Ser. No. 08/409,931 filed Mar. 23,1995, now U.S. Pat. No. 5,659,036, which is a divisional application ofnow abandoned Ser. No. 08/266,639, filed Jun. 28, 1994, abandoned.

FIELD OF THE INVENTION

The present invention relates to a process for producing a2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester having ahigh purity as an important intermediate for the production of aquinacridone pigment, in high yields without purification, and a processfor the production of a quinacridone from the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester.

PRIOR ART OF THE INVENTION

It is known that a 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester as an intermediate for the production of a quinacridonepigment is obtained by polycondensation-reacting1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) with anaromatic amino compound in such amounts that the molar ratio of the1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) to aromaticamino compound is 1/2.

The purity of the above intermediate is a critical factor for producinga quinacridone having a high purity in high yields and for thesubsequent formation of the pigment. For producing a quinacridone, thereis known a method in which 6,13-dihydroquinacridone is synthesized byallowing 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester toundergo a intramolecular-alcohol-elimination, ring-closing reaction at ahigh temperature and oxidized to obtain a quinacridone, or a method inwhich 2,5-di(arylamino)-3,6-dihydroterephthalic acid is synthesized bysaponifying an ester portion and oxidizing a formed central ring andfurther allowed to react with a ring-closing agent to obtain aquinacridone. In both the above methods, the purity of the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester affects theproperties of a quinacridone as an end product when no purificationprocedures are carried out in the course of carrying out the abovemethods.

Therefore, studies have been made to improve the purity of the above2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester or thepurity of other intermediates. Japanese Patent Publication No. 37-18733discloses a method in which succinosuccinic acid diester is synthesizedfrom succinic acid ester in a dialkylcarboxylic acid solvent, anarylamino compound such as aniline and an acid catalyst are added to thereaction mixture and the mixture is allowed to react in nitrogen currentunder atmospheric pressure to obtain a2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester. Thismethod requires an additional step in which water is added to thereaction mixture and the resultant mixture is cooled to precipitate areaction product, since the reaction product is present being dissolvedin the solvent. In this method, therefore, a longer period of time isrequired for the production, and the yield is low, as low as 35 to 85%.

Japanese Patent Publication No. 36-11630 discloses the method in which areaction mixture is directly used for the next step withoutprecipitating 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkylester from the synthesis solvent. In this method,1,4-cyclohexanedione-2,5-di(carboxylic acid ethyl ester) is synthesizedfrom succinic acid ethyl ester in the presence of a mixture of biphenylwith a diphenyl ether as a solvent (commercially available in the tradename of "Dowtherm A"), byproducts dissolved in the reaction mixture areremoved by washing, then, an excess amount of an aromatic amino compoundand a hydrochloric acid salt of an aromatic amino compound of the samekind are added, the intended reaction of the resultant mixture iscarried out under reduced pressure, a nitrogen gas is introduced up toatmospheric pressure when the reaction reaches a final point, and thehydrochloric acid of the solvent is neutralized with sodium carbonate.The so-formed 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkylester is completely dissolved in the "Dowtherm A", and an excess amountof aromatic amino compound is hence distilled off under reduced pressurebefore carrying out the subsequent reaction. In this method, theprocedures from the reaction of succinic acid ethyl ester to theproduction of 6,13-dihydroquinacridone are carried out in one reactor,and the number of production apparatus can be hence decreased. However,the yield of 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkylester is not very high, or 85%, and a large amount of energy and a longperiod of time are required for distilling off an excess of water and anaromatic amino compound. Further, the filtration, washing andpurification are not carried out in the course of the production. Ithence cannot be said that impurities have no influence on the endproduct.

It is made known by JP-A-53-26823 that even a trace amount of adissolved aromatic amino compound has an extraordinary influence on theyield and purity of 6,13-dihydroquinacridone when the6,13-dihydroquinacridone is produced from pure2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester in thepresence of "Dowtherm A". The aromatic amino compound can be separatedfrom "Dowtherm A" to a certain extent by distillation, while it isassumed that the aromatic amino compound cannot be completely separatedby distillation due to the solubility of the aromatic amino compound in"Dowtherm A". Therefore, it is not preferred to carry out the proceduresfrom the reaction of succinic acid ethyl ester through the formation of2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester to theproduction of 6,13-dihydroquinacridone in one reactor in the presence ofthe same solvent.

For overcoming the above defect, JP-A-53-26823 discloses a method inwhich 1,4-cylcohexanedione-2,5-di(carboxylic acid alkyl ester) and anaromatic amino compound are allowed to undergo a condensation reactionin the presence of an inert gas while the aromatic amino compound isused in an excess amount so that it works as a reactant and a solvent,then, an inert solvent having a high boiling point such as "Dowtherm A"is charged, an excess amount of aromatic amino compound is distilled offunder reduced pressure, and a reaction mixture (solution or slurry)containing 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl esterand the inert solvent having a high boiling point such as "Dowtherm A"is fed to exactly the same solvent having a high boiling point which hasbeen heated up to 250° C. or higher thereby to produce6,13-dihydroquinacridone. However, the defect in that an excess amountof the aromatic amino compound is required to be distilled off stillremains to be solved. The above method therefore cannot be said to beindustrially advantageous due to the long period of time required forthe series of operations and many steps required. Further, when oxidizedto a corresponding quinacridone, the 6,13-dihydroquinacridone obtainedby the above method hardly gives a quinacridone having a high productquality due to the influence of a trace amount of the above aromaticamino compound.

Further, JP-B-60-16411 discloses a method in which1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) and an aromaticamino compound are allowed to undergo a condensation reaction in thepresence of an aromatic nitro compound having no substituent in theo-position as a solvent or a diluent. This method also seeks to carryout the subsequent reaction without isolating2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester. When6,13-dihydroquinacridone is produced, not an excess amount of thearomatic amino compound but the presence of the aromatic nitro compoundinhibits the formation of the 6,13-dihydroquinacridone, and the abovemethod is hence disadvantageous.

JP-A-62-205163 (corresponding to U.S. Pat. No. 4,812,568) describes anExample in which a reaction between1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) and an aromaticamino compound is carried out in a reactor in the presence of methanolas a solvent and glacial acetic acid as a catalyst. Since, however, thereactor is not flushed with an inert gas, 2,5-di(arylamino)terephthalicacid dialkyl ester is inevitably formed, and the reaction requires along period of time, as long as 6 hours. Further, since glacial aceticacid used as a catalyst forms almost no salt with the aromatic aminocompound, it is difficult to separate aromatic amino compound and aceticacid from a solution exhausted after filtration and washing. Moreover,glacial acetic acid is used in an amount of 1.3 mol per mole of1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) used as a rawmaterial, or the amount of glacial acetic acid used as a catalyst is toolarge. When the end product is subjected to thin layer chromatographyfor determining the amount of residual materials, the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester has apurity of only 96 to 98%, and the above method is not industriallyefficient.

The intramolecular-alcohol-elimination reaction for forming6,13-dihydroquinacridone from 2,5-di(arylamino)-3,6-dihydroterephthalicacid dialkyl ester is disclosed, for example, in Japanese PatentPublications Nos. 36-11630 and 44-3216, U.S. Pat. No. 2,821,541,Japanese Patent Publication No. 45-16340, JP-A-52-134630, JP-A-52-51400,JP-A-53-26823, JP-B-55-47626, JP-B-57-57749 and JP-A-62-205163. However,the methods disclosed in Japanese Patent Publications Nos. 36-11630,44-3216 and 45-16340 and JP-A-52-134630 only give6,13-dihydroquinacridones having a purity of less than 99%, and show alow conversion, as low as 90%. Byproducts formed in addition to the endproduct, 6,13-dihydroquinacridone, include3-alkoxycarbonyl-2-anilino-1,4-dihydro-9-acridanone,2,5-dianilinoterephthalic acid and3-carboxyl-2-anilino-1,4-dihydro-9-acridanone, and these are liable tobe formed when the alcohol-elimination, ring-closing reaction is carriedout in a solvent having a high boiling point.

U.S. Pat. No. 2,821,541 discloses a method in which2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester issynthesized in "Dowtherm A" and then subjected to a ring-closingreaction by heating it. In this method, however, not only the yield islow, but also it is necessary to carry out the synthesis of2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester while waterformed during the synthesis is removed. Thus, the above method isindustrially disadvantageous.

Further, in JP-A-53-26823, 2,5-di(arylamino)-3,6-dihydroterephthalicacid dialkyl ester is synthesized in a solvent having a high boilingpoint such as "Dowtherm A", aromatic amino compound remaining after thesynthesis is distilled off under reduced pressure, the resultant productis fed to a preheated solvent having a high boiling point, and thering-closing reaction is carried out to obtain 6,13-dihydroquinacridone.In principle, however, the aromatic amino compound is not removed bywashing or cleaning the 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester, and therefore it affects the formation of6,13-dihydroquinacridone all the same.

Further, JP-B-55-47626 discloses methyl naphthalene, biphenyl anddiphenyl oxide as solvents having a high boiling point. However, thesegive lower yields and purities of the product due to their lower boilingpoints than that of "Dowtherm A". JP-A-57-57749 discloses benzyl etheras the above solvent, and JP-A-62-205163 discloses dimethyl diphenylether as the above solvent. However, these Publications fail to definethe purity of 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkylester used and the amount of aromatic amino compound contained therein.Further, the boiling points of the above solvents having a high boilingpoint are not proper, and the results obtained in these Publications arenot satisfactory with regard to the yield, purity and reaction time.

The oxidation of 6,13-dihydroquinacridone is disclosed in Examples of 9to 15 U.S. Pat. No. 2,821,529, Examples 1 to 6 of UK Patent 909602 andExamples 1 to 11 of UK Patent 911477. Since, however, these Patents giveonly quinacridone as coarse particles, there is required a step offorming a pigment for use as a coloring material.

The oxidation of 6,13-dihydroquinacridone proceeds as a solid-liquid orsolid-gas reaction in which particles form cores and are oxidized, sinceit has low solubility in organic solvents. In a practical sense,therefore, it is impossible to obtain quinacridone particles having asmaller size than the dihydroquinacridone particles which are to beoxidized. That is, the step of forming a pigment can be omitted onlywhen 6,13-dihydroquinacridone having a proper size for a pigment isoxidized. The 6,13-dihydroquinacridones obtained by the methodsdisclosed Japanese Patent Publications 36-11630 and 44-3216,JP-A-57-57749, JP-A-62-205163, etc., are of coarse particles having aspecific surface area of 10 m² /g or less, and when these coarseparticles are oxidized by any one of the methods disclosed in JapanesePatent Publications Nos. 36-138333, U.S. Pat. No. 3,007,930,JP-A-53-94334, etc., industrially disadvantageously, it is required toadd a step of forming a pigment.

The oxidation and saponification of2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester into2,5-di(arylamino)terephthalic acid are disclosed, for example, inJP-A-49-108036 and JP-A-51-598301. However, nothing is specifiedconcerning 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl esterused and the influence of byproducts, and the yield and purity of theformed 2,5-di(arylamino)terephthalic acid and the reaction time are notsatisfactory.

Further, the intramolecular-dehydration, ring-closing reaction of2,5-di(arylamino)terephthalic acid, e.g., a method using polyphosphoricacid or sulfuric acid, is disclosed in Japanese Patent Publications Nos.36-17826, 37-14928 and 38-21632, JP-A-53-37730 and JP-B-61-21263. Amethod using a ring-closing agent and a catalyst in the presence of anorganic solvent is disclosed in Japanese Patent Publications Nos.42-5414 and JP-B-56-45434. In the method using polyphosphoric acid orsulfuric acid, however, the form of a crystal varies depending upon themethod of precipitating quinacridone after the ring-closing reaction.Further, when polyphosphoric acid is used, it can be recovered only inthe form of phosphoric acid when water is included, and for convertingthe phosphoric acid into polyphosphoric acid, it is required to addphosphorus pentaoxide. As a result, the amount of polyphosphoric acidgradually increases. Therefore, the above method is not industriallyadvantageous, and further, the yield of quinacridone is not high.Meanwhile, the method using a ring-closing agent and a catalyst in thepresence of an organic solvent has an advantage in that the solvent canbe recovered, while the yield of quinacridone is not high. Further, boththe above ring-closing methods give coarse particles of quinacridone,and industrially disadvantageously, the above methods require asubsequent step of forming a pigment for using the quinacridone as acoloring material.

The present inventors have made diligent studies of optimum reactionconditions for producing 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester most suitable for obtaining quinacridone suitable for useas a pigment through the oxidation of 6,13-dihydroquinacridone orthrough the ring-closing of 2,5-di(arylamino)terephthalic acid, and as aresult, have found optimum reaction conditions on the basis of themixing ratio of 1,4-cyclohexanedione-2,5-di(carboxylic acid alkylester), an aromatic amino compound and a catalyst and the kind of thecatalyst. Further, it has been found that 6,13-dihydroquinacridone or2,5-di(arylamino)terephthalic acid suitable for producing a quinacridonepigment can be obtained from 2,5-di(arylamino)-3,6-dihydroterephthalicacid dialkyl ester under certain conditions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process forproducing 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl esterhaving a high purity from 1,4-cyclohexanedione-2,5-di(carboxylic acidalkyl ester) in high yields for a short period of time.

It is another object of the present invention to provide a process forproducing quinacridone of which the byproduct content is small, from theabove 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester.

Further, it is another object of the present invention to provide aprocess for producing quinacridone of which the particle diameter isadjusted as desired, from the above2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester withoutadding a step of forming a pigment.

According to the present invention, there is provided a process for theproduction of 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkylester by a condensation reaction between1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) and an aromaticamino compound of the formula (1), ##STR1## wherein X is F, Cl, Br, I,--OH, --NO₂, --CF₃, an alkyl group having 1 to 4 carbon atoms, asubstituted alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, a substituted alkoxy group having 1 to 4carbon atoms, a phenyl group, a cyclohexyl group, a phenoxy group,--COOH, a --COO--C₁ -C₄ alkyl group, --SO₃ H, a phenylamino group, abenzamino group, --N(CH₃)₂, --SO₂ HN₂, --SO₂ N(CH₃)₂, a pyridino group,--CONH₂ or --CON(CH₃)₂, and n is an integer of 0 to 4, provided that ahydrogen atom is positioned on at least one ortho-position relative tothe NH₂,

the amount of the aromatic amino compound of the formula (1) being 2.0to 4.0 mol per mole of the 1,4-cyclohexanedione-2,5-di(carboxylic acidalkyl ester),

the said polycondensation reaction being carried out in the presence, asa catalyst, of hydrochloric acid or sulfuric acid in an amount of 0.04to 1.10 mol per mole of the 1,4-cyclohexanedione-2,5-di(carboxylic acidalkyl ester) and in the presence, as a solvent, of a lower alcoholhaving 1 to 4 carbon atoms, in an oxygen-free atmosphere at a reactiontemperature between 80° C. and 130° C.

Further, according to the present invention, there is provided a processfor producing quinacridone, which comprises heating the above-obtained2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester in anorganic solvent up to a temperature between 250° C. and 350° C. in anoxygen-free atmosphere, thereby proceeding with anintramolecular-alcohol-elimination reaction to convert the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester to6,13-dihydroquinacridone, and oxidizing the 6,13-dihydroquinacridone.

Further, according to the present invention, there is provided a processfor producing quinacridone, which comprises oxidizing and saponifyingthe above-obtained 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester to covert the 2,5-di(arylamino)-3,6-dihydroterephthalicacid dialkyl ester to 2,5-di(arylamino)terephthalic acid, and thenheating the 2,5-di(arylamino)terephthalic acid up to a temperaturebetween 100° C. and 180° C. in a sulfuric acid or polyphosphoric acid tocarry out intramolecular dehydration and ring-closing thereof.

Further, according to the present invention, there is provided a processfor producing quinacridone, which comprises oxidizing and saponifyingthe above-obtained 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester to covert the 2,5-di(arylamino)-3,6-dihydroterephthalicacid dialkyl ester to 2,5-di(arylamino)terephthalic acid, mixing the2,5-di(arylamino)terephthalic acid with a ring-closing agent in anorganic solvent slightly miscible with water in the presence of acatalyst, and heating the resultant mixture up to a temperature between150° C. and 210° C. to carry out intramolecular dehydration and ringclosing of the 2,5-di(arylamino)terephthalic acid.

DETAILED DESCRIPTION OF THE INVENTION

The alkyl of the 1,4-cyclohexanedione-2,5-di(carboxylic acid alkylester) used in the present invention is a lower alkyl group having 1 to4 carbon atoms or a substituted alkyl group having 1 to 4 carbon atoms.Specific examples of the alkyl include methyl, ethyl, isopropyl,n-butyl, iso-butyl, sec-butyl and tert-butyl. This alkyl group isdissociated as an alcohol when the intramolecular-alcohol eliminationreaction takes place. The number of carbon atoms of this alkyl group ishence perferably the same as the number of carbon atoms of a solventused, and the purity thereof is preferably at least 99%.

The solvent used in the present invention is a lower alcohol having 1 to4 carbon atoms, and examples thereof include methanol, ethanol,n-propanol, iso-propanol, n-butanol and iso-butanol. When these solventsare used, only a very small amount of1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) as a rawmaterial is dissolved therein at room temperature. However, at thereaction temperature employed in the present invention,1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) can be fullydissolved in the solvent of which the weight is 7 to 14 times as largeas the weight of the raw material. Further, in the temperature range offrom room temperature to the reaction temperature, only a very smallamount of the formed 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester is dissolved therein.

The aromatic amino compound used in the present invention is a compoundof the formula (1) in which a hydrogen atom is positioned in at leastone ortho-position relative to the amino group substituted on thearomatic ring. The substituent (X in the formula (1)) which can besubstituted on the aromatic ring for hydrogen includes F, Cl, Br, I,--OH, --NO₂, --CF₃, an alkyl group having 1 to 4 carbon atoms, asubstituted alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, a substituted alkoxy group having 1 to 4carbon atoms, a phenyl group, a cyclohexyl group, a phenoxy group,--COOH, a --COO--C₁ -C₄ alkyl group, --SO₃ H, a phenylamino group, abenzamino group, --N(CH₃)₂, --SO₂ HN₂, --SO₂ N(CH₃)₂, a pyridino group,--CONH₂ and --CON(CH₃)₂. The number (n in the formula (1)) of the abovesubstituents may be introduced onto the aromatic ring is 0 to 4, and aplurality of these substituents may be the same or different.

The catalyst used in the present invention refers to a generally usedacid such as hydrochloric acid or sulfuric acid. The smaller the amountof water dissolved therein is, the better, since the main reactionproceeds in a dehydration-condensation reaction.

The amount of the aromatic amino compound per mole of the1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) is 2.0 to 4.0mol, and the amount of the catalyst per mole of the1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) is 0.04 to 1.10mol. Preferably, the difference obtained by deducting the molar amountof the catalyst from the molar amount of the aromatic amino compound is2.3 to 2.9 when these molar amounts are calculated on an assumption thatthe molar amount of the 1,4-cyclohexanedione-2,5-di(carboxylic acidalkyl ester) is 1. That is, the amount of the aromatic amino compound isconsidered to be a positive factor which improves the purity and yieldof 2,5-di(arylamino)-3,6-dihydroterephthalic acid to be formed when thisamount is increased, and the amount of the catalyst is considered to bea negative factor which has an adverse effect on the above purity andyield when this amount is increased. Therefore, when the differenceobtained by offsetting these positive and negative factors is in aproper range, the product having the highest purity can be obtained at ahigh yield.

Oxygen is another negative factor. When oxygen is present in thereaction system, 1,4-cyclohexanedione-2,5-di(carboxylic acid alkylester) is completely dissolved in the solvent when the1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) reaches thereaction temperature, and the 1,4-cyclohexanedione-2,5-di(carboxylicacid alkyl ester) is oxidized by dehydrogenation sooner than itundergoes a dehydration condensation reaction with the aromatic aminocompound. Or, when the aromatic amino compound undergoes a condensationwith one molecule of 1,4-cyclohexanedione-2,5-di(carboxylic acid alkylester), the condensate is oxidized by dehydrogenation. Or, the formed2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester is oxidizedby dehydrogenation. In any event, a byproduct other than the intendedproduct is formed. The formation of these byproducts can be prevented byflushing the pressure reactor with an inert gas such as nitrogen, carbondioxide or argon gas before the reactants charged in the pressurereactor are stirred under heat.

1,4-Cyclohexanedione-2,5-di(carboxylic acid alkyl ester), the aromaticamino compound, the catalyst and the solvent in the above-describedamounts are charged into a pressure reactor up to 70% of the totalvolume of the pressure reactor or less, and the pressure reactor isclosed. Then, the pressure in the pressure reactor is increased anddecreased repeatedly with an inert gas to fully replace oxygen with theinert gas, and thereafter, an inert gas is introduced up to a pressureof 0 to 5 kg/cm² at a gage pressure. The reactants aretemperature-increased up to the predetermined reaction temperature, andallowed to react, with stirring at a circumferential speed of 20 to 120m/minute. The reaction proceeds by about 95% for a reaction time of 90minutes, and thereafter it gradually proceeds. Therefore, the reactiontakes about 3 to 5 hours. After the reaction, the reaction mixture isimmediately cooled to room temperature, and an alkali in a minimumamount necessary to neutralize the acid used as the catalyst is added inthe form of an aqueous solution. Then, the reaction mixture is stirredfor a while, and the inert gas increasing the pressure in the pressurereactor is released, the product is filtered, and the filtrate is washedwith a wash liquid until the filtrate becomes transparent. The washliquid is the same lower alcohol as the alcohol used as the solvent, andit is heated up to about 60° C. in advance. In the present invention,the synthesis of 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkylester proceeds at high yields. When the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester formedaccording to the process of the present invention is measured for purityby liquid chromatography and IR, it is found to have a remarkablepurity. This product can be processed into an intermediate for theintended quinacridone by the subsequent reaction even if it containsmethanol or is in the state of an aqueous paste.

The 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl esterobtained according to the above process of the present invention ismixed, for example, with a heating medium commercially available in thetrade name of "Dowtherm A" which is a mixture biphenyl and diphenylether, or with any one of alkylnapthalene, N-methylpyrrolidone, dibenzylether and t-amyl alcohol, and the mixture is heated up to 200° to 350°C. under atmospheric pressure or elevated pressure, whereby the alkylgroup and arylamino group of the ester portion of the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester undergointramolecular-alcohol-elimination and the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester isconverted to a corresponding 6,13-dihydroquinacridone which issubstituted as required.

The corresponding 6,13-dihydroquinacridone substituted as required ispreferably obtained by mixing the above2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester withdimethylnaphthalene isomer mixture of which the weight is 3 to 15 timesas large as that of the 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester, either heating the mixture to a temperature not higherthan 150° C. or bringing the mixture into a non-heated state, andgradually adding the mixture to a dimethylnaphthalene isomer mixture ofwhich the weight is 3 to 15 times as large as that of the mixture andwhich is heated to 200° to 350° C. in advance, under atmosphericpressure or elevated pressure in an oxygen-free atmosphere.

In the above reaction for obtaining 6,13-dihydroquinacridone, oxygenworks as a negative factor as is already explained. Therefore,6,13-dihydroquinacridone having a high purity can be obtained bycarrying out the above reaction in an oxygen-free state.

The 6,13-dihydroquinacridone obtained by the above process of thepresent invention can be converted to a corresponding quinacridone, forexample, by oxidizing the 6,13-dihydroquinacridone with an oxidizingagent such as sodium m-nitrobenzenesulfonate, nitrobenzene,nitronaphthalene, nitrobenzenesulfonic acid, nitrobenzenecarboxylicacid, nitrophenol, oxygen or air, in the presence of a mixed solvent ofmethanol, ethanol, acetone, ethylene glycol or glycol ether with water,in the presence of an alkali, at a high temperature, optionally underelevated pressure, and optionally in the presence of a dispersing agentand a reaction promoter. The oxidation is carried out, for example, withair in the presence of a dispersing agent, preferably an anionicdispersing agent such as a condensate from aromatic sulfonic acid andformaldehyde, and the quinacridone is formed as coarse particles. Forusing these particles of quinacridone as a coloring material, it isrequired to carry out a so-called pigmentation step of converting thecoarse particles to fine particles.

The oxidation of 6,13-dihydroquinacridone is a solid-liquid reaction ora solid-gas reaction in which particles of 6,13-dihydroquinacridoneforms cores and are oxidized since the 6,13-dihydroquinacridone has lowsolubility in organic solvents. It is hence practically impossible toobtain quinacridone particles having a smaller size than that of thedihydroquinacridone to be oxidized. In other words, the pigmentationstep can be omitted only when 6,13-dihydroquinacridone particles havinga size smaller than the size suitable as a pigment are oxidized.

However, the 6,13-dihydroquinacridone obtained by the above process ofthe present invention gives an unconventional quinacridone substitutedas required, which does not require the pigmentation step, by a methodin which the 6,13-dihydroquinacridone is converted to a salt in asolution containing 40 to 96% by weight of a lower alcohol having 1 to 4carbon atoms, 4 to 30% by weight of sodium hydroxide or potassiumhydroxide and 0 to 30% by weight of water, either mineral acid or waterand an alcohol are added so that the resultant mixture has aconcentration of an alkali which amount is equal to, or lower than, astoichiometric amount and that the salt is hydrolyzed, thereby to obtain6,13-dihydroquinacridone having a specific surface area of at least 20m² /g and having a uniform size, and the so-obtained6,13-dihydroquinacridone is oxidation-treated with an oxidizing agentselected from nitrobenzenesulfonic acids, anthraquinonesulfonic acids,sodium polysulfide and oxygen in a C₁ -C₄ lower alcohol solutioncontaining 1.5 to 20% by weight of sodium hydroxide and 2 to 40% byweight of water.

In the above method, the purity of 6,13-dihydroquinacridone is critical.Almost no publications which have been available describe the purity of6,13-dihydroquinacridone to be oxidized. When a byproduct formed duringthe dehydration condensation reaction between1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) and thearomatic amino compound remains in the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester, thebyproduct inhibits the conversion of the2,5-di(arylamino)-3,6-dihydroterephthlalic acid dialkyl ester to6,13-dihydroquinacridone and causes the formation of a new byproduct. Asa result, the 6,13-dihydroquinacridone has a low purity. When6,13-dihydroquinacridone having a byproduct content of 1% or more isconverted to a salt and oxidized in an alcohol-alkali solvent, thegrowth of particles and the oxidation are greatly prevented, and nodesirable particle form is obtained. When such 6,13-dihydroquinacridoneis oxidized according to the above process of the present invention, theoxidation rate is very low, and only a quinacridone having a low purityis obtained. This byproduct has a low solubility in organic solvents asdescribed already, and it is hence difficult to remove the byproduct. Itis therefore important to control the reaction so that the abovebyproduct is not formed.

In contrast, 6,13-dihydroquinacridone containing no byproduct and havinga high purity easily forms a salt in an alcohol solution in the presenceof an alkali. That is because >C═O groups bond to Na and K as is thecase with quinacridone, it is clear that an alkali is required in anamount of at least 2 mol (at least a stoichiometric amount) per mole of6,13-dihydroquinacridone. The formed salt of 6,13-dihydroquinacridone ishydrolyzed by decreasing the amount of an alkali to less than thestoichiometric amount. Particles of 6,13-dihydroquinacridone formed bythe above hydrolysis are obtained as fine particles which have aspecific surface area of at least 20 m² /g and are easily oxidized,whereby an excellent quinacridone pigment can be obtained.

The above process of the present invention is the most preferablycarried out as follows. That is, 6,13-dihydroquinacridone having a highpurity is charged into a proper reactor having a stirrer and a refluxdevice together with a lower alcohol having 1 to 4 carbon atoms and anecessary amount of a water-soluble alkali. When the mixture is stirred,the 6,13-dihydroquinacridone and the alkali form a salt. The solvent(lower alcohol) includes methanol, ethanol, n-propanol, iso-propanol,n-butanol and iso-butanol, while methanol is preferred. Thewater-soluble alkali includes potassium hydroxide and sodium hydroxide,while sodium hydroxide is preferred in view of easiness in forming thesalt, economic performance and easiness in controlling particles. Forimproving the solubility of the alkali in the mixture, it is preferredto add a small amount of water (preferably the same amount as that ofthe alkali). The amount of the solvent (alcohol+water-solublealkali+water) is 3 to 30 times, preferably 5 to 15 times, as large asthe weight of the 6,13-dihydroquinacridone. The solvent contains 40 to96% by weight of the alcohol, 4 to 30% by weight of the water-solublealkali and 0 to 30% by weight of water, preferably contains 70 to 88% byweight of the alcohol, 6 to 20% by weight of the water-soluble alkaliand 6 to 20% by weight of water. The salt formation proceeds at arelatively high rate, while the salt is easily formed when the alkaliconcentration is high. When the 6,13-dihydroquinacridone is formed intoa salt, it becomes a large crystal having a size of about 30 μm. Afterthe salt is formed, a mineral acid such as sulfuric acid or hydrochloricacid, water or alcohol is added to the solution containing the abovecrystal, whereby the crystal is hydrolyzed to give fine6,13-dihydroquinacridone particles having a specific surface area of 20to 40 m² /g.

For the oxidation, the solvent solution containing the above hydrolyzed6,13-dihydroquinacridone is adjusted to an alcohol solution containing1.5 to 20% by weight of the water-soluble alkali and 2 to 40% by weight,preferably 2 to 30% by weight, of water. When the solvent solution hasan alkali concentration less than a salt-forming concentration, theoxidation may be initiated without adjusting the alkali concentration.However, when the solvent solution has an alkali concentration higherthan the salt-forming concentration, the 6,13-dihydroquinacridone formsa salt again, and no intended pure quinacridone substituted as requiredis obtained. The oxidizing agent is selected from nitrobenzenesulfonicacids, anthraquinonesulfonic acids, sodium polysulfide and oxygen. Aboveall, sodium m-nitrobenzenesulfonate is preferred, since the oxidationproceeds moderately. A strong oxidizing agent such as oxygen is liableto promote the oxidation and form quinacridone-quinone. When the alkaliconcentration is adjusted to 1.5 to 20% by weight for the oxidation,there are obtained quinacridone particles which are uniform and have aspecific surface area of 10 to 40 m² /g.

The purity of 6,13-dihydroquinacridone (unsubstituted) is measured, forexample, by the following method.

Dihydroquinacridone content (wt%)=0.205×(Abs241-0.527×Abs598-2.93×B)/A×100

B=Abs440-0.047×Abs598

Abs241=absorbance at 241 nm

Abs440=absorbance at 440 nm

Abs598=absorbance at 598 nm

A sample is weighed in an exact amount of 4 mg (exactness of 0.01 mg,this weight is referred to as A (mg)), and dissolved in special-gradesulfuric acid in a 100-ml measuring flask to prepare a constant volume.The sample was measured for absorbance at 24° to 26° C. with a 1 cmthick quartz cell, and sulfuric acid is used as a reference liquid.

The 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl esterproduced according to the present invention can be converted to acorresponding 2,5-di(arylamino)terephthalic acid by treating it in amixed solvent of a solvent with water in the presence of an oxidizingagent and an alkali, at a high temperature, optionally under elevatedpressure and optionally in the presence of a dispersing agent and areaction promoter. The above oxidizing agent includes sodiumm-nitrobenzenesulfonate, nitrobenzene, nitronaphthalene,nitrobenzenesulfonic acid and nitrophenol. The above solvent includesmethanol, ethanol, acetone, ethylene glycol and glycol ether.

Further, the 2,5-di(arylamino)terephthalic acid obtained by the aboveprocess of the present invention can be converted to a correspondingquinacridone by heating the 2,5-di(arylamino)terephthalic acid up to100° to 180° C. while mixing it with polyphosphoric acid orultraphosphoric acid of which the weight is 5 to 20 times as large asthat of the 2,5-di(arylamino)terephthalic acid. In this process, the2,5-di(arylamino)terephthalic acid undergoes anintramolecular-dehydration, ring-closing reaction to be converted to acorresponding quinacridone. Or, the 2,5-di(arylamino)terephthalic acidcan be converted to a corresponding quinacridone by a method in whichthe 2,5-di(arylamino)terephthalic acid is mixed with a ring-closingagent and an acid catalyst or an organic catalyst in an organic solventslightly miscible with water and the mixture is heated up to 150° to210° C., whereby the 2,5-di(arylamino)terephthalic acid undergoes anintramolecular-dehydration, ring-closing reaction to be converted to acorresponding quinacridone. The above ring-closing agent includesnitrobenzene, nitronaphthalene, aniline, phosgene, benzoyl chloride andethylene glycol. The above acid catalyst includes hydrochloric acid andacetic acid. The above organic catalyst includes quinoline.

When the 6,13-dihydroquinacridone is oxidized or when the2,5-di(arylamino)terephthalic acid is allowed to undergo anintramolecular-dehydration, ring-closing reaction, 1 to 20% by weight ofa quinacridone pigment derivative such as a basic quinacridone pigmentderivative disclosed in JP-A-2-123168 (corresponding to U.S. Pat. No.5,368,641) or an acidic or neutral quinacridone pigment derivative ofthe following formula (2) may be added, whereby a quinacridone pigmenthaving an adjusted desirable crystal state can be obtained and thequinacridone pigment can be imparted with advantageous surfaceproperties and practically advantageous properties. ##STR2## wherein Qis an unsubstituted quinacridone residue or a quinacridone residuesubstituted with a halogen atom, an alkyl group having 1 to 4 carbonatoms, an alkoxy group having 1 to 4 carbon atoms, H₂ N--CO-- or a C₁-C₄ alkyl-NH--CO-- group, each of X₁ and X₂ is independently a hydrogenatom, a halogen atom (when X₁ and X₂ are hydrogen atoms and halogenatoms, each of i and j is an integer of at least 2, or one of thesubstituents of the following formulae (3), and each of i and j isindependently an integer of 1 to 4), ##STR3## wherein Y is a hydrogenatom, a halogen atom, --NO₂ or --SO₃ H, M is a hydrogen atom, a calciumatom, a barium atom, a strontium atom or an aluminum atom, each of R₃,R₄, R₅ and R₆ is a hydrogen atom (excluding a case where all of R₃, R₄,R₅ and R₆ are hydrogen atoms) or an alkyl group having 1 to 30 carbonatoms, k is an integer of 1 to 4, and m is a valence of M.

Further, when the 6,13-dihydroquinacridone is oxidized or when the2,5-di(arylamino)terephthalic acid is allowed to undergo anintramolecular-dehydration, ring-closing reaction, a quinacridone havinga desired crystal form may be added, whereby a quinacridone having adesired crystal form can be obtained.

The following quinacridones can be synthesized according to the presentinvention.

Quinacridone, 2,9-dichloroquinacridone, 3,10-dichloroquinacridone,4,11-dichloroquinacridone, 2,3,9,10-tetrachloroquinacridone,2,4,9,11-tetrachloroquinacridone, 2,9-difluoroquinacridone,2,9-dibromoquinacridone, 2,9-dimethylquinacridone,3,10-dimethylquinacridone, 4,11-dimethylquinacridone,2,4,9,11-tetramethylquinacridone, 2,9-di(tert-butyl)quinacridone,2,9-dihydroxylquinacridone, 2,9-di(trifluoromethyl)quinacridone,2,9-dimethoxyquinacridone, 2,9-diethoxyquinacridone,2,4,9,11-tetramethoxyquinacridone, 2,9-dicarboxylquinacridone,2,9-dichlorohexylquinacridone, 2,9-diphenylquinacridone,2,9-di(dimethylamino)quinacridone,2,9-di(dimethylaminosulfo)quinacridone,2,9-di(dimethylaminocarbonyl)quinacridone, 3,10-dinitroquinacridone,2,9-dimethyl-4,11-dichloroquinacridone,2,9-dimethyl-4,11-dicarboxyquinacridone, and 2,9-dipyridinoquinacridone.

The quinacridone obtained in the present invention is remarkablyexcellent in weatherability and masking properties, and it can be usedin a paste, a flash color, a print coloring material, a lacquer, aperoxide curing varnish and a polyurethane varnish. The quinacridoneobtained in the present invention can be incorporated into synthetic andnatural polymers. These polymers include thermoplastic resins such aspolyvinyl chloride, polystyrene, polyethylene, polyester, phenolplast,aminoplast and rubber. Further, the quinacridone obtained in the presentinvention can be incorporated into natural, recycled and synthetic fibermaterials, and it can be also incorporated into organic and inorganicpigments.

A mixture containing the quinacridone obtained in the present inventionas a coloring component may be any one of a solid, an elastomer, a pasteand a viscous material. An aqueous paste is obtained, for example, byadding a wetting agent or a dispersing agent to the pigment and stirringthe mixture in water, or by adding the pigment to a dispersing agent anddispersing or kneading the mixture in the presence of water andoptionally an organic solvent or an oil. This paste can be used forproducing a flash color, a print coloring material, an aqueous coatingcomposition, a plastic dispersion and a spinning liquid. Thequinacridone obtained in the present invention can be incorporated intowater, an organic solvent, a non-drying oil, a drying oil, a lacquer, avarnish, a plastic and rubber by stirring, roll-stirring, kneading ormilling.

The present invention will be explained hereinafter with reference toExamples, in which "part" stands for "part by weight" and "%" stands for"% by weight".

EXAMPLE 1

A 1-liter autoclave of pressure glass was charged with 45.60 parts (0.2mol) of 1,4-cyclohexanedione-2,5-di(carboxylic acid methyl ester) welldried, 46.57 parts (0.5 mol) of aniline, 500 parts of methanol and 4.65parts (0.045 mol) of 35% hydrochloric acid, and the autoclave wastightly closed. Then, oxygen in the autoclave was fully replaced withnitrogen gas, and the pressure in the autoclave was set at a gagepressure of 0 kg/cm². While the mixture was vigorously stirred, thetemperature in the autoclave was increased from room temperature to 100°C. over 15 minutes, and then the mixture was allowed to react for 3hours. The highest pressure in the autoclave during the reaction was 3.8kg/cm². The reaction mixture was cooled to 30° C. or lower, and then,the pressure was released to a level of atmospheric pressure. 18 Partsof a 10% NaOH aqueous solution was charged, and after the mixture wasstirred for 10 minutes, the reaction product was filtered. The resultantcake was fully washed with methanol having a temperature of 60° C. Theyield of the formed 2,5-dianilino-3,6-dihydroterephthalic acid dimethylester was 75.07 parts, which was 99.3% of the theoretical yield.Further, the purity thereof was 99.5%.

Comparative Example 1

A 1-liter flask having a condenser and a nitrogen-introducing tube wascharged with 45.60 parts (0.2 mol) of1,4-cyclohexanedione-2,5-di(carboxylic acid methyl ester), 46.57 parts(0.5 mol) of aniline, 500 parts of methanol and 4.65 parts (0.045 mol)of 35% hydrochloric acid, and oxygen in the flask was fully replacedwith nitrogen gas. Then, while the mixture was vigorously stirred, thetemperature in the flask was increased from room temperature to boilingpoint of 65° C. over 15 minutes, and the mixture was allowed to reactfor 3 hours. The reaction mixture was cooled to 30° C. or less, andthen, 18 parts of a 10% NaOH aqueous solution was charged. Then, themixture was stirred for 10 minutes, the reaction product was filtered,and fully washed with methanol having a temperature of 60° C. The yieldof the formed 2,5-dianilino-3,6-dihydroterephthalic acid dimethyl esterwas 72.46 parts, which was 95.8% of the theoretical yield. Further, thepurity thereof was 94.3%.

Comparative Example 2

Comparative Example 1 was repeated except that the amount of aniline waschanged to 39.49 parts (0.424 mol) and that the amount of 35%hydrochloric acid was changed to 6.96 parts (0.067 mol). The yield ofthe formed 2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester was66.54 parts (88.02% of the theoretical yield). Further, the puritythereof was 97.4%.

EXAMPLE 2

Example 1 was repeated except that the amount of aniline was changed to51.41 parts (0.552 mol) and that the amount of 35% hydrochloric acid waschanged to 1.25 parts (0.012 mol). The yield of the formed2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester was 75.22parts (99.50% of the theoretical yield). Further, the purity thereof was99.4%.

EXAMPLE 3

Example 1 was repeated except that the aniline was replaced with 69.56parts (0.545 mol) of p-chloroaniline, to give 88.24 parts (98.7% of thetheoretical yield) of 2,5-di(p-chloroanilino)-3,6-dihydroterephthalicacid dimethyl ester. The purity thereof was 99.5%.

Comparative Example 3

Comparative Example 1 was repeated except that the aniline was replacedwith 69.56 parts (0.545 mol) of p-chloroaniline, to give 84.39 parts(94.4% of the theoretical yield) of2,5-di(p-chloroanilino)-3,6-dihydroterephthalic acid dimethyl ester. Thepurity thereof was 95.1%.

EXAMPLE 4

Example 1 was repeated except that the aniline was replaced with 58.39parts (0.545 mol) of p-toluidine, to give 80.31 parts (98.9% of thetheoretical yield) of 2,5-di(p-toluidino)-3,6-dihydroterephthalic aciddimethyl ester. The purity thereof was 99.6%.

Comparative Example 4

Comparative Example 1 was repeated except that the aniline was replacedwith 58.39 parts (0.545 mol) of p-toluidine, to give 76.41 parts (94.1%of the theoretical yield) of 2,5-di(p-toluidino)-3,6-dihydroterephthalicacid dimethyl ester. The purity thereof was 94.6%.

EXAMPLE 5

Example 1 was repeated except that the1,4-cyclohexanedione-2,5-di(carboxylic acid methyl ester) was replacedwith 51.2 parts (0.2 mol) of 1,4-cyclohexanedione-2,5-di(carboxylic acidethyl ester) and that the methanol was replaced with 500 parts ofethanol, to give 80.14 parts (98.7% of the theoretical yield) of2,5-dianilino-3,6-dihydroterephthalic acid diethyl ester. The puritythereof was 99.4%.

EXAMPLE 6

Example 1 was repeated except that the 35% hydrochloric acid wasreplaced with 4.50 parts (0.045 mol) of 98% sulfuric acid, to give 73.71parts (97.5% of the theoretical yield) of2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester. The puritythereof was 99.0%.

EXAMPLE 7

Example 1 was repeated except that the methanol was replaced with 500parts of n-propanol and that the reaction temperature was set at 120°C., to give 74.16 parts (98.1% of the theoretical yield) of2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester. The puritythereof was 99.1%.

EXAMPLE 8

Example 1 was repeated except that the methanol was replaced with 500parts of iso-butanol and that the reaction temperature was set at 120°C., to give 74.39 parts (98.4% of the theoretical yield) of2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester. The puritythereof was 99.2%.

Comparative Example 5

Example 1 was repeated except that the methanol was replaced with 500parts of 2-methyl-1-pentanol and that the reaction was carried out at aboiling point of 136° C. under atmospheric pressure, to give 71.74 parts(94.9% of the theoretical yield) of2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester. The puritythereof was 97.6%.

EXAMPLE 9

30 Parts of the 2,5-dianilino-3,6-dihydroterephthalic acid dimethylester obtained in Example 1 and 150 parts of a dimethylnaphthaleneisomer mixture were charged into a 200-ml flask having an outlet valvein the bottom, and the mixture was heated up to 120° to 170° C. withstirring under nitrogen gas atmosphere. Then, the resultant hot mixturewas added to 150 parts of the same dimethylnaphthalene isomer mixture asthat used above in a 500 ml-flask over 20 to 40 minutes, whichdimethylnaphthalene isomer mixture was stirred under nitrogen gasatmosphere and maintained at 280° C. Then, the mixture was furthermaintained at 280° to 283° C. (reflux) for 30 minutes.

On adding the hot mixture of 2,5-dianilino-3,6-dihydroterephthalic aciddimethyl ester with the dimethylnaphthalene isomer mixture, which hotmixture had a temperature of 120° to 170° C., to the dimethylnaphthaleneisomer mixture, the reaction for the formation of6,13-dihydroquinacridone was initiated while methanol was generated, andthe generation of methanol almost finished immediately after the refluxat 283° C. was initiated.

The reaction mixture was cooled to 100° C., and then the nitrogen gasatmosphere was removed. The reaction mixture was filtered, washed with500 ml of hot methanol and dried to give 24.47 parts (98.2 % of thetheoretical yield) of 6,13-dihydroquinacridone. The6,13-dihydroquinacridone was measured for a purity by IR and absorbanceto show at least 99%.

Comparative Example 6

Example 9 was repeated except that the2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester used inExample 9 was replaced with 30 parts of the2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester obtained inComparative Example 1, to give 23.5 parts (94.5% of the theoreticalyield) of 6,13-dihydroquinacridone. The 6,13-dihydroquinacridone wasmeasured for a purity by IR and absorbance to show 96.8%.

EXAMPLE 10

Example 9 was repeated except that the dimethylnaphthalene isomermixture used in Example 9 was replaced with a mixed solvent commerciallyavailable in the trade name of "Dowtherm A", to give 24.3 parts (97.5%of the theoretical yield) of 6,13-dihydroquinacridone. The6,13-dihydroquinacridone was measured for a purity by IR and absorbanceto show at least 99%.

Comparative Example 7

Example 10 was repeated except that the2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester used inExample 10 was replaced with 30 parts of the2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester obtained inComparative Example 1, to give 22.2 parts (89.1% of the theoreticalyield) of 6,13-dihydroquinacridone. The 6,13-dihydroquinacridone wasmeasured for a purity by IR and absorbance to show 96.2%.

EXAMPLE 11

79 Parts of methanol and 12 parts of a 50% NaOH aqeuous solution werefully stirred in a flask of stainless steel. 10 Parts of the6,13-dihydroquinacridone obtained in Example 9 and 10 parts of sodiumm-nitrobenzenesulfonate were gradually added, and the mixture wasrefluxed at 70° to 75° C. for 3 to 5 hours. The mixture was cooled untilit had a temperature of 40° C. or lower, and the mixture was filtered.The resultant cake was washed with hot water until the wash water wascolorless and transparent, and dried, to give 9.78 parts (98.4% of thetheoretical yield) of an unsubstituted quinacridone. The quinacridonewas measured for a purity by IR and absorbance to show 99.2% ofquinacridone and 0.8% of 6,13-dihydroquinacridone. The quinacridone hada specific surface area of 22.8 m² /g.

Comparative Example 8

Example 11 was repeated except that the 6,13-dihydroquinacridone used inExample 11 was replaced with the 6,13-dihydroquinacridone obtained inComparative Example 6, to give 9.69 parts (97.5% of the theoreticalyield) of an unsubstituted quinacridone. The quinacridone was measuredfor a purity by IR and absorbance to show 96.7% of quinacridone and 2.9%of 6,13-dihydroquinacridone. Further, the so-obtained quinacridone wasformed into a coating composition, the coating composition was comparedwith a coating composition from the quinacridone obtained in Example 11to show a color difference of ΔE=2.4 and that the coating compositionfrom the quinacridone in this Example was yellowish and dull. Thequinacridone had a specific surface area of 35.4 m² /g.

EXAMPLE 12

Example 11 was repeated except that the sodium m-nitrobenzenesulfonatewas replaced with sodium anthraquinone-β-sulfonate, to give 9.69 parts(97.5% of the theoretical yield) of an unsubstituted quinacridone. Thequinacridone was measured for a purity by IR and absorbance to show98.9% of quinacridone and 0.7% of 6,13-dihydroquinacridone. Further, theso-obtained quinacridone was formed into a coating composition, thecoating composition was compared with a coating composition from thequinacridone obtained in Example 11 to show a color difference of ΔE=0.4and that the coating composition from the quinacridone in this Examplewas bluish but clear. The quinacridone had a specific surface area of24.1 m² /g.

EXAMPLE 13

8.9 Parts of 2,5-di(p-chloroanilino)-3,6-dihydroterephthalic aciddimethyl ester, 50 parts of ethanol, 5.37 parts of KOH, 24.35 parts ofwater and 6 parts of sodium m-nitrobenzenesulfonate were charged into a200-ml flask of stainless steel, and refluxed with stirring for 10hours. When the suspension changed to a black solution, ethanol wassteam-distilled, and the reaction mixture was filtered to remove asolid. The remaining solution was heated up to 80° C. with stirring, andafter 35 parts of a 10% hydrochloric acid aqueous solution was dropwiseadded, the mixture was maintained for 1 hour. Then, the mixture wasfiltered, washed with hot water and dried to give 8.21 parts (98.4% ofthe theoretical yield) of 2,5-di(p-chloroanilino)terephthalic acid.

Comparative Example 9

Example 13 was repeated except that the2,5-di(p-chloroanilino)-3,6-dihydroterephthalic acid dimethyl ester usedin Example 13 was replaced with 8.94 parts of the2,5-di(p-chloroanilino)-3,6-dihydroterephthalic acid dimethyl esterobtained in Comparative Example 3, to give 7.72 parts (92.6% of thetheoretical yield) of 2,5-di(p-chloroanilino)terephthalic acid.

EXAMPLE 14

Example 13 was repeated except that the sodium m-nitrobenzenesulfonatewas replaced with air and that the reaction was carried out while theair was blown into a solution in the flask at 20 ml/minute during thereaction, to give 8.02 parts (96.2% of the theoretical yield) of2,5-di(p-chloroanilino)terephthalic acid.

EXAMPLE 15

7.51 Parts of 2,5-di(p-chloroanilino)terephthalic acid obtained inExample 13, 79 parts of nitrobenzene, 6 parts of benzoyl chloride and1.65 parts of quinoline were charged into a 200-ml flask of stainlesssteel, and maintained at 200° C. for 5 hours. When the mixture wastemperature-increased up to about 180° C., hydrochloric acid gas wasgenerated and the intramolecular-dehydration reaction was initiated. Thereaction mixture was cooled to 110° C., and then 2.27 parts of 30%sodium hydroxide was dropwise added to decompose an excess of benzoylchloride. Then, the reaction mixture was filtered while it was hot,washed with methanol, washed with water and dried to give 6.37 parts(92.8% of the theoretical yield) of 2,9-dichloroquinacridone.

Comparative Example 10

Example 15 was repeated except that the2,5-di(p-chloroanilino)terephthalic acid used in Example 15 was replacedwith 7.51 parts of the 2,5-di(p-chloroanilino)terephthalic acid obtainedin Comparative Example 9, to give 5.95 parts (86.7% of the theoreticalyield) of 2,9-dichloroquinacridone.

EXAMPLE 16

10 Parts of the 6,13-dihydroquinacridone obtained in Example 9 and 80parts of methanol were charged into a 200-ml flask having a refluxer,and stirred. 12 Parts of a 50% NaOH aqueous solution was added, and themixture was stirred at 40° C. for 30 minutes to form a salt. 26 Parts of10% sulfuric acid was added dropwise to hydrolyze the salt, and thereaction mixture was refluxed under heat for 1 hour. 10 Parts of sodiumm-nitrobenzenesulfonate was added, and immediately therafter, 3 parts ofa 50%. NaOH aqeuous solution was added. Then, the mixture was refluxedfor 4 hours to give 9.82 parts (98.8% of the theoretical yield) of anunsubstituted quinacridone having an excellent particle diameter as apigment.

EXAMPLE 17

10 Parts of the 6,13-dihydroquinacridone obtained in Example 9 and 80parts of methanol were charged into a 200-ml flask having a refluxer,and stirred. 12 Parts of a 50% NaOH aqueous solution was added, and themixture was stirred at 40° C. for 30 minutes to form a salt. 26 Parts of10% sulfuric acid was added dropwise to hydrolyze the salt, and thereaction mixture was refluxed under heat for 1 hour. 10 Parts of sodiumm-nitrobenzenesulfonate was added, and immediately therafter, 50 partsof a 50% NaOH aqeuous solution was added. Then, the mixture was refluxedfor 4 hours to give 9.88 parts (99.4% of the theoretical yield) of anunsubstituted quinacridone having an excellent particle diameter as apigment.

EXAMPLE 18

10 Parts of the 6,13-dihydroquinacridone obtained in Example 9 and 80parts of methanol were charged into a 200-ml flask having a refluxer,and stirred. 12 Parts of a 50% NaOH aqueous solution was added, and themixture was stirred at 40° C. for 30 minutes to form a salt. 40 Parts of10% sulfuric acid was added dropwise to hydrolyze the salt, and thereaction mixture was refluxed under for 1 hour. 10 Parts of sodiumm-nitrobenzenesulfonate was added, and the mixture was refluxed for 4hours to give 9.76 parts (98.2% of the theoretical yield) of anunsubstituted quinacridone having an excellent particle diameter as apigment.

Comparative Example 11

10 Parts of the 6,13-dihydroquinacridone obtained in Example 9 and 80parts of methanol were charged into a 200-ml flask having a refluxer,and stirred. 12 Parts of a 50% NaOH aqueous solution was added, and themixture was stirred at 40° C. for 30 minutes to form a salt. 40 Parts of10% sulfuric acid was added dropwise to hydrolyze the salt, and thereaction mixture was refluxed under heat for 1 hour. 10 Parts of sodiumm-nitrobenzenesulfonate was added, and the mixture was refluxed for 4hours to give 9.41 parts (94.7% of the theoretical yield) of anunsubstituted quinacridone. The quinacridone was measured for a purityby IR and absorbance to show 91.2% of quinacridone and 8.8% of6,13-dihydroquinacridone.

EXAMPLE 19

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with 93.74 parts (0.545 mol) of p-bromoaniline, to give 96.59parts (90.1% of the theoretical yield) of2,5-di(p-bromoanilino)-3,6-dihydroterephthalic acid dimethyl ester. Thepurity thereof was 98.0%.

EXAMPLE 20

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with 2,4-dichloroaniline, to give2,5-di(2,4-dichloroanilino)-3,6-dihydroterephthalic acid dimethyl ester.The purity thereof was 98.0%.

EXAMPLE 21

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with 2-chloro-4-methylaniline, to give2,5-di(2-chloro-4-methylanilino)-3,6-dihydroterephthalic acid dimethylester. The purity thereof was 98.4%.

EXAMPLE 22

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with p-phenylaniline, to give2,5-di(p-phenylanilino)-3,6-dihydroterephthalic acid dimethyl ester. Thepurity thereof was 97.3%.

EXAMPLE 23

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with 4-trifluoromethylaniline, to give2,5-di(4-trifluoromethylanilino)-3,6-dihydroterephthalic acid dimethylester. The purity thereof was 97.8%.

EXAMPLE 24

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with p-carboxylaniline, to give2,5-di(p-carboxylanilino)-3,6-dihydroterephthalic acid dimethyl ester.The purity thereof was 98.1%.

EXAMPLE 25

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with 2,3,4,5-tetrachloroaniline, to give2,5-di(2,3,4,5-tetrachloroanilino)-3,6-dihydroterephthalic acid dimethylester. The purity thereof was 94.2%.

EXAMPLE 26

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with p-sulfoaniline, to give2,5-di(p-sulfoanilino)-3,6-dihydroterephthalic acid dimethyl ester. Thepurity thereof was 97.8%.

EXAMPLE 27

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with p-dimethylaminocarbonylaniline, to give2,5-di(p-dimethylaminocarbonylanilino)-3,6-dihydroterephthalic aciddimethyl ester. The purity thereof was 94.8%.

EXAMPLE 28

Example 1 was repeated except that the aniline used in Example 1 wasreplaced with p-dimethylaminoaniline, to give2,5-di(p-dimethylaminoanilino)-3,6-dihydroterephthalic acid dimethylester. The purity thereof was 95.2%.

EXAMPLE 29

Example 13 was repeated except that the2,5-di(p-chloroanilino)-3,6-dihydroterephthalic acid dimethyl ester usedin Example 13 was replaced with 7.56 parts of2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester, to give 6.88parts (98.9% of the theoretical yield) of 2,5-dianilinoterephthalic aciddimethyl ester.

EXAMPLE 30

A 200-ml flask was charged with 6.96 parts of the2,5-dianilinoterephthalic acid obtained in Example 29 and 70 parts ofsulfuric acid having a concentration of 98%, and while the mixture wasstirred, the mixture was maintained at 160° C. for 5 hours. Then, themixture was cooled to 80° C. or lower, and 50 parts of water wasgradually added over 4 hours. Then, the mixture was poured into 500parts of ice-containing water at one stroke, and the mixture wasfiltered, washed with water and dried to give 5.83 parts (93.5% of thetheoretical yield) of an unsubstituted quinacridone.

In the process for producing 2,5-di(arylamino)-3,6-dihydroterephthalicacid dialkyl ester, provided by the present invention,1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) and thearomatic amino compound are condensation-reacted in a completelydissolved and uniform state by heating a solvent in which1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) is notdissolved at room temperature and at a boiling temperature, the1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) and thearomatic amino compound up to a temperature higher than the boilingpoint in a pressure reactor, whereby the degree of completeness of thereaction is improved and a product having a high purity can be obtained.

Further, the solubility of the product,2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester, obtainedby the process of the present invention in a lower alcohol having 1 to 4carbon atoms such as methanol and ethanol is much lower than thesolubility of the reactant, 1,4-cyclohexanedione-2,5-di(carboxylic acidalkyl ester) at a boiling point and at the reaction temperature employedin the present invention, and the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester henceeasily precipitates in the above lower alcohol. Further, impurities andthe unreacted reactant have properties of being easily dissolved in theabove lower alcohol. Therefore, the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester can beeasily isolated by filtration, and the amount of the solvent for washingthe product can be decreased.

The 2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl esterobtained by the process of the present invention has a remarkably highpurity, and therefore, 6,13-dihydroquinacridone and2,5-di(arylamino)terephthalic acid having a high purity can be obtainedat high yields in the subsequent processes for the production thereof.Further, the corresponding quinacridone having a high purity can be alsoobtained at high yields by the subsequent reaction.

Quinacridones obtained by prior art techniques have a defect in thatsince the particles thereof are coarse or very fine aggregates, theyrequire a pigmentation step, while quinacridones substituted asrequired, obtained in the present invention, easily permits the crystaltransition and particle control by a series of steps.

What is claimed is:
 1. A process for producing quinacridone whichcomprises(1) producing 2,5-di(arylamino)-3,6-dihydroterephthalic aciddialkyl ester by a condensation reaction between1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester) and an aromaticamino compound of the formula (1), ##STR4## wherein X is F, Cl, Br, I,--OH, --NO₂, --CF₃, an alkyl group having 1 to 4 carbon atoms, an alkoxygroup having 1 to 4 carbon atoms, a phenyl group, a cyclohexyl group, aphenoxy group, --COOH, a --COO--C₁ -C₄ alkyl group, --SO₃ H, aphenylamino group, a benzamino group, --N(CH₃)₂, --SO₂ HN₂, --SO₂N(CH₃)₂, a pyridino group, --CONH₂ or --CON(CH₃)₂, and n is an integerof 0 to 4, provided that a hydrogen atom is positioned in at least oneortho-position relative to the NH₂, the amount of the aromatic aminogroup of the formula (1) being 2.0 to 4.0 mol per mole of the1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester), the saidcondensation reaction being carried out in the presence, as a catalyst,of hydrochloric acid or sulfuric acid in an amount of 0.04 to 1.10 molper mole of the 1,4-cyclohexanedione-2,5-di(carboxylic acid alkyl ester)and in the presence, as a solvent, of a lower alcohol having 1 to 4carbon atoms, in an oxygen-free atmosphere at a reaction temperaturebetween 80° C. and 130° C., after which the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester isisolated, (2) oxidizing the 2,5-di(arylamino)-3,6-dihydroterephthalicacid dialkyl ester in a solution of 1.5 to 20% by weight of awater-soluble alkali and 2 to 40% by weight of water in a lower alcoholhaving 1 to 4 carbon atoms to convert the2,5-di(arylamino)-3,6-dihydroterephthalic acid dialkyl ester to2,5-di(arylamino)terephthalic acid, which is isolated, and (3) carryingout intramolecular dehydration and ring-closing thereof.
 2. A processaccording to claim 1, wherein the oxidizing is carried out in thepresence of at least one member selected from the group consisting ofnitrobenzenesulfonic acid, anthraquinonesulfonic acid and sodiumpolysulfide.
 3. A process according to claim 1, wherein theintramolecular dehydration and ring-closing is carried out by heatingthe 2,5-di(arylamino)terephthalic acid up to a temperature of between100° and 180° C. in a sulfuric acid or polyphosphoric acid.
 4. A processaccording to claim 1, wherein the intramolecular dehydration andring-closing is carried out by mixing the 2,5-di(arylamino)terephthalicacid in an organic solvent slightly miscible with water in the presenceof a catalyst, and heating the resultant mixture up to a temperaturebetween 150° and 210° C.